Wide interest in underwater sports stimulates creation of cavitating cores for sport shooting at underwater marks and for underwater hunting with arbalests, harpoon guns and firearms.
The need in creating cavitating cores arises from the fact that harpoon arrows for arbalests and harpoon guns slow down in the water and quickly stop due to the viscous fluid hydrodynamic drag, and available bullets intended for firing in the air loose their stability after entering the water and come to stop at the range of 0.5-0.7 m.
There is information about 4.5 mm and 5.66 mm ammunitions with a caliber bullet made in the form of a cavitating core with the length of more than 21 calibers. The core travels in the water stably due to the formation of a natural cavity, but is not stabilized for flight in the air (see IVANOV V. N. “ZNIITOCHMASH—razrabotchik patronov”—VPK: Voenny Parad (Military Parade), 01/02 2001, page 38 . . . 39, hereinafter referred as “IVANOV”, CHIKIN A. M. “Morskie Diavoly”—Moscow, “Veche” Publishers, 2003, page 272 . . . 275, hereinafter referred as “CHIKIN”, ARDASHEV A. N., FEDOSEEV S. L., “Oruzhie spetsialnoe, neobychlloe, exoticheskoe”—Moscow, “Voennaya technika” Publishers, 2001, page 172 . . . 177, hereinafter referred as “ARDASHEV et al.”).
To hit targets successfully in the atmosphere and in the aquatic environment cavitating cores must retain their stability while moving both in the air and in the water, as well as must smoothly pass the interface (air-water and water-air).
Stable flight of the cavitating core in the air is provided by its aft part that may have the form of a multiblade empennage at aerodynamic stabilization. And at spin-stabilization it may have a cone-cylindrical form to give gyroscopic stability to the core.
From technical literature it is known that high-speed movement of the cavitating core in the water is accompanied by the formation of a natural cavity, which widens behind the cavitating edge of the core secant nose part. The contour of that cavity is close to the ellipsoid of revolution, its end parts corresponding to the asymptotic law of jet spread and being constant on the most part of the underwater trajectory (see GUREVICH M. I. “Teoria struy idealnoy zhidkosti”—Moscow, Physical-mathematical Literature Publishing, 1961, page 160 . . . 168, 410 . . . 460, hereinafter referred as “GUREVICH”, YAKIMOV Yu. L. “Ob integrate energii pri dvizhenii s malymi tchislami kavitatsii I predelnyh formah kaverny”—Academy of Science of the USSR, Fluid and Gas Mechanics, No. 3, 1983, page 67 . . . 70).
It is also well known that the largest cavity diameter Dκ depends on the cavitation number σ, cavitating edge diameter d and its cavitating drag index cx:Dκ=d×(Cx/σ)0.5 The cavitation number σ depends on the hydraulic pressure P and water density ρ, as well as on the water vapor pressure in the cavity (P0˜0.02 kg/cm2) and core velocity V:σ=2×(P−P0)/ρ×V2 The cavity length depends on its largest diameter Dκ:Lκ=Dκ×σ−0.5×(ln σ−1+ln ln σ−1)0.5 
Initial cavity dimensions are in large excess over the dimensions of the core. For example, the length of cavitating cores of ammunition for sporting and hunting guns is 25 . . . 60 mm, while for the core velocity of 800 m/s the length of the cavity at the depth of 2 m is more than 13 m and for the core velocity of 500 m/s the length of the cavity at the depth of 2 m is more than 5 m. The length of end parts of the cavity (forward and rear sections) makes up 10% of its total length; their contour is constant and corresponds to the asymptotic law of jet spread.
Stabilization of the core in the cavity is provided by its aft part due to one-sided periodic washing and gliding along the cavity contour with its gliding surface; therefore the largest diameter of the circle that circumscribing the cross-section of the aft part defines the cavitating core caliber.
Scattering on the underwater trajectory depends on the geometry of the core head part, which is affected by water particles that escape from cavitating edge and also on the depth and the area of inertial washing of the core aft part gliding surface that defines the value of the one-sided gliding drag.
When the central or the head part is washed in the cavity, the core loses its stability, tumbles and slows down by the lateral surface.
Moving in the cavity, the core loses its energy to overcome the cavitation drag F:F=cx×π×d2×ρ×V2/8
The core velocity V on the underwater distance S depends on its mass m, initial velocity V0 and cavitation drag F:V=V0×e−s×F/m 
With the drop of the core velocity V the cavitation number σ grows and the cavity dimensions Lκ and Dκ reduce; moreover, with the depth increase the dimensions reduction and the cavity collapse on the core aft part occur earlier, at a higher velocity V and at a shorter distance S.
In the course of the cavity collapse, besides the cavitation drag F, there also appears the fluid viscous drag on the core surface that significantly increases the total hydrodynamic resistance.
In accordance with hydrodynamics laws the range of targets hitting under the water could be increased by raising the core mass m, as well as by reducing the cavitating edge diameter d and the index of its cavitation drag cx. For these purposes the cavitating core contour must correspond to the contour of the cavity forward part, which has a constant volume along the most part of the underwater trajectory.
A cavitating core intended for firing from special weapon is known firm publications (see Description to patent RU 2112205, Int. Cl.6 F42B 30/02, published May 27, 1998). The head part of the core with a flat secant nose surface has the form of a truncated cone; central and aft parts are cylindrical and correspond to the weapon caliber. For stabilization in the air the core head part is made of tungsten alloy and the central part and aft part with tail empennage of aluminum. The contour of this core corresponds to the geometry of known cavitating cores for 4.5 mm ammunition (see IVANOV, CHIKIN ARDASHEV et al.), therefore under the water the core is stabilized in the formed cavity.
The disadvantage of that cavitating core with the length of more than 21 calibers lies in its geometry, as for its correspondence to the cavity contour, the cavitating edge diameter should be increased; that results in the formation of a cavity with an oversized volume, and an extended gap between the gliding surface and the cavity contour promotes significant angular oscillations and deep inertial washing of narrow blades of the tail empennage. The above mentioned disadvantages result in the growth of scattering along the underwater trajectory and in the reduction of underwater targets hitting range.
There is information about a cavitating core intended for firing from firearms with the use of a discarding sabot. In this core the conical head part with a cylindrical section is conjugated with the flat secant nose surface along the cavitating edge. The central cylindrical part has circular grooves for fixation in the discarding sabot, and the aft part is made in the form of a multiblade empennage with triangular fins having a sharp edge on the gliding surface (See Description to U.S. Pat. No. 5,955,698, Int. Cl.6 F42B 15/20, published on Sep. 9, 1999).
The disadvantage of this known design lies in the fact that the cavitating core contour is significantly understated relative to the cavity contour; that reduces the mass and strength of the core. A sharp edge on the gliding surface of empennage blades is subjected to deep washing due to its small area, and that results in the increased gliding drag. The gap between the core and the cavity contour at the base of the core head part is substantially reduced, so water particles that escape from the cavitating edge exert additional impact on the head part. The above mentioned disadvantages result in the growth of scattering along the underwater trajectory and in the reduction of underwater targets hitting range.
The closest analog (prototype) of this claimed invention is a cavitating core intended for shooting from firearms with the use of a discarding sabot. The cavitating core has a head part conjugated with a secant nose surface along the cavitating edge, a central part and an aft part with a gliding surface; the caliber of the cavitating core is defined by the maximum diameter of the circle circumscribing the aft part cross-section. In the plane of the core axial longitudinal section the apex angle of tangents to the secant nose surface in the points of its conjugation with the head part is 60°-18°, and the enveloping contour of the core cross-sections is confined by the outline of three conjugated truncated cones inscribed into the contour of the cavity formed. Stabilization of the cavitating core in the air may be provided by rotation or by the aft empennage (See Description to patent RU 2268455, Int. Cl.7 F42B 10/38, published on Jan. 1, 2006).
The disadvantage of this known design lies in the fact that the contour of three conjugated truncated cones cannot correspond to the cavity outline exact approximation, so the cavitating core geometry is not optimal, and the cavitating core mass is always understated, hence underwater targets hitting range is also reduced. Besides, this cavitating core design cannot be used without a discarding sabot for shooting from arbalests and harpoon gulls, as well as from firearms.